Developing a climatology of convective precipitating patterns in Africa

The prediction of convective precipitation remains one of the greatest problems in weather forecasting. In recent decades, our understanding of the lifecycles of convective precipitating systems has been expanded by the use of satellite and radar observations. Recent studies of warm-season precipitation in the United States and East Asia have found that clusters of heavy precipitation display coherent patterns of propagation in the continental United States and East Asia. This study examines the propagation and evolution of convective precipitation in Africa.

Digitized images from the European geostationary satellite (Meteosat) for a multi-year period (starting with May to August 1999) are used to document convective episodes over Africa. The infrared images have a spatial resolution of 5km at the satellite sub-point and are available at 30 minute intervals. The continent is divided into two domains for tracking precipitating cloud systems. The northern domain encompasses 5ºS to 20ºN and 20ºW to 40ºE from May to September. The southern domain covers 35ºS to 5ºN and 5ºE to 40ºE from October to April. Hovmoller strips of 0.1 degree longitude are drawn through each domain and a threshold technique is used to identify the cold cloud systems that are most likely to be precipitating. Comparisons of IR and corresponding water vapor images help to distinguish between deep layer moisture associated with precipitating thunderstorms and a drier layer with primarily cirrus. In addition, images from the Tropical Rainfall Measurement Mission (TRMM) satellite are used to differentiate rain areas. Given the similarity in the lifecycles of mesoscale convective systems in other continents, coherent patterns are expected for Africa as well. This study will provide detailed information on those coherent patterns specific to convection in Africa.